do not ignore user configured JAVA_HOME

Patch by eevans; reviewed by Michael Shuler for CASSANDRA-6131
Fix dropping columns in trunk

patch by Mikhail Stepura; reviewed by Aleksey Yeschenko for
CASSANDRA-6520
Move *PropDefs to o.a.c.cql3.statements
Merge branch 'cassandra-2.0' into trunk
replace SnapTreeMap/AtomicSortedColumns with BTree/AtomicBTreeColumns
patch by Benedict Elliott Smith; reviewed by jbellis for CASSANDRA-6271